(1) Field of the Invention
This invention relates to phthalocyanine compounds, and particularly to phthalocyanine compounds capable of showing absorption in the near infrared range.
(2) Description of the Related Art
Cyanine compounds, various metal compounds and the like have conventionally been known as absorptive materials in the near infrared and infrared range. These compounds are however generally unstable to light and heat.
On the other hand, phthalocyanine compounds are very stable to light, heat, moisture, etc. and have excellent fastness. Owing to their high stability and intense tones, they have been found wide-spread utility as various dyes or pigments. They are also interesting, for example, as materials for dark conduction, photoconduction or energy conversion, materials such as electrodes and catalysts, and high molecular materials suited for use in the production of films or thin films having a high-degree function when blended with a high molecular substance. A variety of investigation is hence under way in this respect. Such phthalocyanine compounds however have difficulties in forming them into films, especially, by spin coating, because their solubility in an organic solvent is low.
Liquid crystal displayers have been proposed, which make use of electro- and thermooptical effects of a liquid crystal having a smectic phase as a liquid-crystal material having thermooptical effects or electro- and thermooptical effects and permit input of information by a near infrared light source such as a light pen equipped with a semiconductor laser and electrical read-out of the information thus inputted.
In a displayer of the above-described type, positioning of a light pen on its liquid crystal display panel results in focusing of a laser beam on a heat-absorbing film on a heating electrode, so that localized generation of heat is induced and the heat is then conducted to a liquid-crystal material in the vicinity of the heat-absorbing film to heat the liquid-crystal material. The liquid-crystal material is tentatively transformed into an isotropic liquid phase in the above-described manner and after movement of the light pen, the thus-heated liquid-crystal material is allowed to cool back into the smectic phase again. Here, domains presenting strong scattering of light in the liquid crystal are formed.
It is hence possible to create a scattered state, in other words, to write or draw characters or a pattern in accordance with movement of the light pen.
This method is however accompanied by a drawback that the efficiency of heat utilization is low, since the heat generated in the heat-absorbing film must be conveyed to the liquid-crystal material by conduction so as to heat the liquid-crystal material. Large laser power has thus been needed for writing information.
As one method for eliminating this drawback, it has been proposed to mix a pigment capable of showing absorption near laser wavelengths (in the near infrared range) as disclosed in the article entitled "A Semiconductor Laser Addressed Dye Doped Liquid Crystal Light Valve " reported in Proc. of the 3rd International Display Research Conference, pp 486-489 (1984). This method has however not been practised because the pigments known to date are not satisfactory in their solubility in a liquid-crystal material and/or in their light fastness.